过滤函数filter

>>> def validate(usernames):
if (len(usernames) > 4) and (len(usernames) < 12):
return usernames

>>> print filter(validate, ('admin', 'maxianglin', 'lin', 'adm', 'wanglili','linghu'))
('admin', 'maxianglin', 'wanglili', 'linghu')
>>>